The hip joint, known as well as the acetabulofemoral joint, is a ball and socket synovial joint that provides an articulation site for the head of the femur with the acetabulum of the pelvis. It mainly functions to support the weight of the body in both dynamic and static positions.
At its most basic, the hip joint serves as a connection of the lower extremity with the axial skeleton. It allows for movement in three major axes, all of which are perpendicular to one another. The center of the entire axis is located at the femoral head. The transverse axis, or left right, allows for flexion and extension. The longitudinal axis, or vertically along the thigh, allows for internal and external rotation. The sagittal axis, or forward to backward allows for abduction and adduction.
In addition to movement, its major function is to weight bear. Hip stability arises from a number of factors, the first of which is the shape of the acetabulum. Due to the depth of the acetabulum, it can encompass almost the entire head of the femur. There is an additional fibro cartilaginous collar surrounding the acetabulum, the acetabular labrum, which provides an even greater articular surface providing further stability. Four additional ligaments are responsible for reinforcing the joint. The pubofemoral, ischiofemoral, and iliofemoral are all extracapsular with attachments to the pubis, ischium, and ilium respectively serving the major focus of preventing an excess range of motion. The pubofemoral ligament prevents excess abduction and extension, ischiofemoral prevents excess extension, and the iliofemoral prevents hyperextension. The remaining ligament, the ligamentum teres (ligament head of the femur) is located intracapsular and attaches to the acetabular notch and the fovea on the femoral head. It serves as a carrier for the foveal artery which supplies the femoral head. Injuries to the ligamentum teres can occur in dislocations, which can cause lesions of the foveal artery, resulting in osteonecrosis of the femoral head.
By 4-6 weeks gestational age, the hip joint begins to develop from the mesoderm. By seven weeks gestational age, a cleft forms in the precartilage cells which are programmed to form the femoral head and acetabulum. By 11 weeks gestational age, the hip joint is formed for the most part. The acetabular cartilage completely encircles the femoral head.
There are numerous variations in the blood supply to the hip. The most common variant results in blood supply coming from the medial circumflex and lateral circumflex femoral arteries, each of which is a branch of the profunda femoris (deep artery of the thigh). The profunda femoris is a branch of the femoral artery which travels posteriorly. There is an additional contribution from the foveal artery (artery to the head of the femur), a branch of the posterior division of the obturator artery, which travels in the ligament of the head of the femur. The foveal artery allows for avascular necrosis to be avoided when medial and lateral circumflex arteries are disrupted. There are two significant anastomoses. The cruciate anastomosis, which supports the upper thigh, and the trochanteric anastomosis which supports the head of the femur.
Lymphatic drainage from the anterior aspect drains to the deep inguinal nodes, while the medial and posterior aspects drain into the internal iliac nodes.
The hip joint receives innervations from the femoral, obturator, superior gluteal nerves.
Muscles of the hip joint can be grouped based upon their functions in relation to the movements of the hip.
Total hip arthroplasty (THA) is an elective procedure for patients with hip pain due to joint space deterioration resulting from numerous conditions. It is a highly effective procedure shown to relieve pain and restore function and improve quality of life in these patients. THA is indicated for patients who have failed other conservative methods including corticosteroid injections, physical therapy, weight reduction, or previous surgical treatment.
The arthroplasty itself consists of three components, a femoral component, an acetabular component, and a bearing surface. Fixation of these prosthetic components requires the use of cement or solely bony ingrowths in cases where cement is not used.
Multiple approaches have been developed for the procedure. The posterolateral approach, also known as the Kocher-Langenbeck approach splits the gluteus maximus muscle, entering the joint posterior thru the capsule. The gluteus medius and minimus are left intact. The anterior approach, also known as the Smith-Petersen approach can gain entry to the joint without any detachment of muscles. Instead, an interval is made between the tensor fasciae latae and the sartorius, from which the joint is accessed anteriorly. The new evidence is showing that the anterior approach may have lower dislocation rates since none of the surrounding muscles are dethatched.
The postoperative stay is typically 1 to 2 days, some recent reports of outpatient procedures are beginning to surface. Physical therapy and mobilization are encouraged as soon as possible to facilitate the healing process as well as preventing DVTs. Timelines for full recovery vary from patient to patient, but most patients are doing well with minimal pain by three months postoperatively.
Congenital Hip Dislocation
Also known as developmental dysplasia of the hip, this can arise when there are problems with the development of the hip joint in utero. Risk factors include breech presentation, positive family history, and oligohydramnios. Diagnosis can be made via physical exam with the Barlow and Ortolani maneuvers which are used to assess joint stability. Additional common findings are leg length asymmetry as well as asymmetric inguinal skin folds. The ultimate goal of treatment is the open or closed reduction of the femoral head back into the acetabulum. The earlier treatment is initiated, the better the outcomes. Mild cases can correct spontaneously by 2 weeks. When subluxation persists more than 2 weeks, treatment is indicated. A standard treatment is the use of the Pavlik Harness which positions the hips into flexion and abduction for 6 weeks full-time followed by 6 weeks part-time.
Commonly seen in the setting of trauma, a posterior dislocation of the hip is most common due to the relatively weak Ischiofemoral Ligament which is located posteriorly. The femoral head in forced posterior, and tears thru the joint capsule resulting in the affected limb to be rotated medially and shortened. Can be further differentiated into simple versus complex where the simple is purely a dislocation, while complex also involved a fracture in the acetabulum or proximal femur. The positioning of the hip often determines the associated acetabular injury. Increased flexion and adduction commonly favor simple posterior dislocation. Patients will typically present with acute pain and inability to bear weight. Approximately 10% of cases may have concurrent damage to the sciatic nerve. Treatment consists of both nonoperative and operative measures. In the acute setting, the emergent closed reduction is recommended within 6 hours of the injury. Irreducible dislocations, those with evidence of incarcerated fragments, and delayed presentations are treated via operative open reduction. Open reduction with internal fixation is recommended for complex dislocations with evidence of acetabular or femoral fractures.
Osteoarthritis of the Hip
Most commonly presents in adults, greater than 40 years old. Symptoms include restricted movement, pain, aches, and stiffness, commonly unilateral. The pain is typically felt in the anterior groin, occasionally including the buttocks and lateral thigh. Some patients can develop generalized hip referred pain of the knee. The pathogenesis involves wear and tear on the joint cartilage, which over time, leads to decreased protective joint space. As bones begin to rub on one another, they attempt to make up for the lost cartilage and form bone spurs or osteophytes. Nonsurgical treatments involve lifestyle modifications such as weight loss, or minimizing activates that exacerbate pain. Physical therapies, the use of assistive devices, and medications such as NSAIDs, acetaminophen, and corticosteroids have also been shown to help. For patients whose pain is still irretraceable, surgical intervention may need to be required. Surgical options include osteotomy, hip resurfacing, and total hip replacement.